CMake: find_library result depends on selected compiler? - linux

Question

I'm confused about how find_library is supposed to work, and I don't know if this could be a CMake bug, or a misuse or misconfiguration on my part. I have installed both GCC and PGI compilers, and when I try this simple CMakeLists.txt file (with both 2.8.11 and 3.5.1):
cmake_minimum_required(VERSION 2.8.11)
find_library( LIBdl dl )
message("LIBdl ${LIBdl}")
I get the following:
$ CC=gcc CXX=g++ cmake .
-- The C compiler identification is GNU 4.8.4
-- The CXX compiler identification is GNU 4.8.4
-- Check for working C compiler: /usr/bin/gcc
-- Check for working C compiler: /usr/bin/gcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++
-- Check for working CXX compiler: /usr/bin/g++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
LIBdl /usr/lib/x86_64-linux-gnu/libdl.so
-- Configuring done
-- Generating done
-- Build files have been written to: /home/molcas-test/test/cmake
That's OK, but:
$ CC=pgcc CXX=pgc++ cmake .
-- The C compiler identification is PGI 17.1.0
-- The CXX compiler identification is PGI 17.1.0
-- Check for working C compiler: /opt/pgi/linux86-64/17.1/bin/pgcc
-- Check for working C compiler: /opt/pgi/linux86-64/17.1/bin/pgcc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working CXX compiler: /opt/pgi/linux86-64/17.1/bin/pgc++
-- Check for working CXX compiler: /opt/pgi/linux86-64/17.1/bin/pgc++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
LIBdl LIBdl-NOTFOUND
-- Configuring done
-- Generating done
-- Build files have been written to: /home/molcas-test/test/cmake
Note dl was not found.
Leaving out either pgcc or pgc++ causes the library to be found, so it must be something in how the compilers are configured. And yet just compiling from the command line finds dl without complain:
$ pgcc -ldl hello_world.c -o hello_world
$ ./hello_world
Hello world!
So I believe something's not right if pgcc can find the library and CMake can't. I could of course set LIB=/usr/lib/x86_64-linux-gnu before running cmake, to force a search in that directory, but that doesn't feel right.
It seems the problem is with gcc. I get /lib/x86_64-linux-gnu included in CMAKE_C_IMPLICIT_LINK_DIRECTORIES, so CMAKE_LIBRARY_ARCHITECTURE is set. But with pgcc this directory is absent and CMAKE_LIBRARY_ARCHITECTURE is empty.
And the directory is missing with pgcc, because pgcc -v doesn't include a -L/lib/x86_64-linux-gnu flag, while gcc -v does. However, ld finds libraries in the directory in either case.
So CMake is not searching libraries in the same places as ld. Should it? Is there an easy way to change this, other than, e.g., manually inspecting all files in /etc/ld.so.conf.d and setting the LIB environment variable?